Abstract

The reactions of 1,1,3,3-tetramethylindane-2-thione (1) with (S)-2-methyloxirane ((S)-2) and (R)-2-phenyloxirane ((R)-6) in the presence of a Lewis acid such as BF3·Et2O, SnCl4, ZnCl2 or SiO2 in dry CH2Cl2 led to the 1,3-oxathiolanes ((S)-3) and ((R)-4) with Me at C(5′) and C(4′), and to (S)-7 with Ph at C(4′), respectively (Schemes 2 and 3). The SiO2-catalyzed reaction of 4,4-dimethyl-2-phenyl-1,3-thiazole-5(4H)-thione (8) with (R)-6 gave two diastereoisomers ((5S,8S)-9) and ((5R,8S)-9) (Scheme 4). In the case of adamantane-2-thione (10) and (S)-2 or (R)-6 with ZnCl2 or SiO2 as catalysts, (S)-11 and (R)-12 with Me at C(5′) and C(4′), respectively, and (S)-13 with Ph at C(4′), were formed. In addition, an unexpected isomer ((R)-14) with Ph at C(5′) and 1,3-dioxolane ((S)-15) were isolated as minor products (Schemes 5 and 6). The structure of (S)-13 was confirmed by X-Ray crystallography (Figure 1). These results show that the SiO2-catalyzed addition of oxiranes to C=S bonds proceeds with high regio- and stereoselectivity via an SN2-type mechanism.

Abstract

The reactions of 1,1,3,3-tetramethylindane-2-thione (1) with (S)-2-methyloxirane ((S)-2) and (R)-2-phenyloxirane ((R)-6) in the presence of a Lewis acid such as BF3·Et2O, SnCl4, ZnCl2 or SiO2 in dry CH2Cl2 led to the 1,3-oxathiolanes ((S)-3) and ((R)-4) with Me at C(5′) and C(4′), and to (S)-7 with Ph at C(4′), respectively (Schemes 2 and 3). The SiO2-catalyzed reaction of 4,4-dimethyl-2-phenyl-1,3-thiazole-5(4H)-thione (8) with (R)-6 gave two diastereoisomers ((5S,8S)-9) and ((5R,8S)-9) (Scheme 4). In the case of adamantane-2-thione (10) and (S)-2 or (R)-6 with ZnCl2 or SiO2 as catalysts, (S)-11 and (R)-12 with Me at C(5′) and C(4′), respectively, and (S)-13 with Ph at C(4′), were formed. In addition, an unexpected isomer ((R)-14) with Ph at C(5′) and 1,3-dioxolane ((S)-15) were isolated as minor products (Schemes 5 and 6). The structure of (S)-13 was confirmed by X-Ray crystallography (Figure 1). These results show that the SiO2-catalyzed addition of oxiranes to C=S bonds proceeds with high regio- and stereoselectivity via an SN2-type mechanism.

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